Calculating squares around the grid

In Maths, we've been working on how to solve the squares around the grid. We came up with 6 ways to calculate it and we've used a 10 by 10 grid.
Here are 3 ways to do it:


My theory for working out the number of the squares is counting the boxes in the top of the grid and in the bottom. Next, you double them. You also do the same on the side of the grid. After you have the answer, you subtract them.
(Remember you can only count the boxes in the edge once)

Example: The number of squares in the top and at the bottom is 10.
(double it) 10 x 10 = 100
In both sides of the grid, there are 8 squares
(double it) 8 x 8 = 64
Now, you subtract them.
100 - 64 = 36

Other methods


In this method, we had to count the boxes on each side of the square. The reason why I used 9 because in each side there are 10 boxes but if we don't count the corners twice, we have 9.
For example 9 + 9 + 9 + 9 = 36
In algebra:
n-1 + n-1 + n-1 + n-1 = 36






The second method is adding the two bottom rows and the 2 sides together.
We only count the corners once that's why we have 8 as the side rows.
For example 10 + 10 + 8 + 8 = 36
If we use algebra as a calculation, it will look like this:
n + n + n-2 + n-2 = 36




Do you know any other way to do it?